Proceedings of the 2020 Mississippi Water Resources Conference

Year: 2020 Authors: Feng G., Reginelli D.

Cover cropping is considered to be an effective management practice for improving dryland soybean yield, water use efficiency (WUE) and soil health. There is a growing interest among producers to adopt cover cropping. However, research data comparing the effectiveness of cover cropping under diverse weather conditions are very limited, particularly in the southern United States. It is important because cover crop species provide specific benefits to crops and soils under various weather conditions. Therefore, both field trials and simulation studies were conducted to evaluated dryland soybean yield and water use, properties and water conservation of a silt loam soil from growing wheat cover crop (CC) followed by corn and soybeans under wet, normal and dry years in the northeast Mississippi. Annual total precipitation averaged 1,373mm in the past 8 decades of seasonal years (1938-2017). In wet years (0 < rainfall probability<25%), annual precipitation ranged from 1,562 to 2,053 mm, and from 1,120 to 1,545 mm in normal years (25% < rainfall probability<75%), and from 821 to 1181 mm in dry years (75% < rainfall probability<100%). Average annual precipitation across wet years was 35% (446 mm) higher than that across normal years, and 69% (701 mm) higher than across all dry years. An 80-yr of RZWQM-simulation demonstrated that, during autumn and spring (early October to early April) and compared to no CC scenario, planting CC reduced drainage deep percolation by 69 mm (11%), 53 mm (15%), and 51 mm (21%) and in wet, normal, and dry years, respectively. When averaged across 40 years and compared to no CC scenario, planting CC decreased surface evaporation by 38 mm (24%) and increased main crop soybean transpiration by 15%. Planting CC increased soybean yield by 41 kg ha^-1; and improved soybean grain WUE by 5%. Cover crops can increase soil organic matter by 15% and storage of rain water in soils by 13% during the crop growing season. Long-term use of winter wheat cover crop, if managed similarly, can reduce deep percolation and increase soil water storage, as well as improve precipitation use efficiency without sacrificing cash crop growth in maize and soybean crop rotations in subtropical agro-systems.